Intravenous administration of pharmacologically active agents offers rapid and direct equilibration with the blood stream which carries the medication to the rest of the body. To decrease the side effects of the intravenous administrated agents, encapsulation of agents to micro- or nano-particles is a useful method. In one aspect, intravenous injection of the therapeutic particles would allow gradual release of the drugs inside the intravascular compartment. In another aspect, drugs in the therapeutic particles would be target delivered when the therapeutic particles are made from target materials.
Some methods of preparing protein particles, such as those used by Abraxane® (U.S. Pat. No. 6,749,868, U.S. Pat. No. 5,560,933), homogenized a mixture of protein solution and organic solvent to form an emulsion, and then subjected the emulsion to a high pressure homogenizer. Under the high pressure, albumin will form a shell around the paclitaxel particle center. Besides the complexity of these methods, high pressure and relatively high temperature are required for obtaining nanoparticles and removing organic solvent. Use of organic solvents is undesirable due to its toxicity and the need to control residual. In addition, drug loading capabilities are limited likely due to the limitation of relying on physical forces to open disulfide bridges. Meanwhile, due to the high pressure and shearing force during the preparation, proteins or peptides may denature permanently, and therefore may lose their bioactivity.
Protein particles have been reported in the literatures as carriers of pharmacologically or diagnostic agents. Microspheres of albumin have been prepared by either heat crosslinking or chemical crosslinking. For instance, the literature has disclosed the use of albumin as a drug carrier for taxanes, including paclitaxel and doxorubicin derivatives. [See Journal of Controlled Release 132 (2008) 171-183; Advanced Drug Delivery Reviews 60 (2008) 876-885]. Further, additional references have disclosed the use of protein cages for drug delivery [Small 5 (2009) 1706-1721]. However, the drug delivery systems cited in the literature are limited by their drug loading capacity as well as limitations as to the therapeutic agents that may be incorporated into the drug delivery systems.
Heat crosslinked microspheres are produced from an emulsified mixture (e.g., albumin, the agent to be incorporated, and suitable oil) at temperatures between 100° C. and 150° C. The microspheres are then washed with a suitable solvent and stored. Leucuta et al. [International Journal of Pharmaceutics Vol. 41:213-217 (1988)] describe the method of preparation of heat crosslinked microspheres.
The procedure for preparing crosslinked microspheres, as described in the literature [Science Vol. 213:233-235 (1981)] and U.S. Pat. No. 4,671,954, uses glutaraldehyde to crosslink the protein chemically, followed by washing and storage.
The reported methods for preparation of protein nanoparticles provide difficulty in encapsulating water-insoluble agents. This limitation is caused by the method itself that relies on crosslinking of proteins in the aqueous phase of an emulsion. Any aqueous-soluble agent dissolved in the protein-containing aqueous phase may be entrapped within crosslinked protein matrix, but a poorly water-soluble or oil-soluble agent cannot be incorporated into a protein matrix formed by these techniques. Furthermore, the protein used for encapsulation is often already denatured and their bioactivity is easily lost during the preparation.